1. Field of the Invention
This invention relates to zoom lenses of high range and small size suited to lens-shutter cameras, video cameras, etc. and, more particularly, to zoom lenses of shortened back focal distance which have attained a shortening of the total length of the lens (the distance from the front vertex to the image plane) and are excellent in portability.
2. Description of the Related Art
Recently, along the trend to advance the reduction of the bulk and size in the lens-shutter cameras, video cameras, etc. has come a demand for zoom lenses of reduced size with a shortening of the total length. Of these zoom lenses, the one including the standard angle of view (the total angular field coverage: 2.omega.=47 degrees, or, in reduction to the 35 mm still camera, the focal length: 50 mm or thereabout) and having a relatively small size is proposed in, for example, Japanese Laid-Open Patent Applications Nos. Sho 63-271214 and Sho 64-72114.
These publications disclose the so-called 3-component zoom lens comprising, from front to rear, a first lens unit of negative refractive power, a second lens unit of positive refractive power and a third lens unit of negative refractive power, these three lens units being moved each forward under a certain condition to provide a zoom ratio of about 2, as zooming from the wide-angle end to the telephoto end.
The zoom lenses have generally a feature that strengthening of the refractive power of every lens unit reduces the required amount of movement of each of the lens units for obtaining the predetermined zoom ratio. By relying on this, it becomes possible to shorten the total length of the lens. The mere increase of the refractive power of every lens unit, however, results in an increase of the range of variation of aberrations with zooming. Particularly in application to the case of greatly extending the range, there is a problem of increasing the difficulty of obtaining a good optical performance throughout the entire zooming range.